This is a brief overview of the technology of nonlinear optical polymers (NLOP) and their use in electro-optic (EO) modulators. This paper also covers preliminary results from the authors' laboratories on highly active CLD- and FTC-type chromophores in guest-host films of APC amorphous polycarbonate. Emphasis will be given to thermal stability and long-term EO modulator aging.

This paper reports the results of two separate heavy ion irradiation experiments. In the first set, nanomaterial samples including single and multi wall carbon nanotubes and electrospun carbon nanofibers, with well-graphitized vapor grown carbon fibers as controls, were irradiated using a primary beam of Krypton-86 ions at 142 Amp MeV. The single and multi wall carbon nanotube samples sustained little damage from the highest radiation dose. In the second set, a gallium nitride nanowire-based field effect transistor was irradiated using a primary beam of Krypton-78 ions at 140 Amp MeV. The nanocircuit maintained normal function under high active bias and high radiation dose. Krypton-86 and Krypton-78 are representative of high-Z heavy ions encountered in a space radiation environment. Results from the pre-irradiation structure and optoelectronic characterization of the gallium nitride nanowires are also reported.

The effects of ionizing radiation on linear and nonlinear optic (NLO) polymer materials and devices for widespread application in photonic systems are discussed herein. Of particular interest are the interaction of electrons, gamma-rays and protons with electro-optic (EO) materials and components. As will be discussed in the paper, various polymer-based thin film materials and components have shown varying resistance to ionizing radiation. Brief explanations for the radiation induced alteration of material and component refractive indices, polarizations, propagation losses, EO coefficient (r33) and SHG are suggested and discussed for proton and gamma-ray irradiations.

We have proposed the concept of photonic DNA computing, which utilizes light and DNA, as a new evolution of parallel computing technology. The scheme has potential for achieving ingenious information processing by use of the properties of light including spatial parallelism and visibility, and the nature of DNA such as reaction parallelism and capability for autonomous reactions. We are developing optical techniques to realize this idea. An important example is the parallel optical manipulation technique that uses vertical-cavity surface-emitting laser (VCSEL) array sources. One can generate various optical field distributions by directly modulating the optical outputs of individual VCSELs, and it is possible to achieve manipulation of microscopic objects without physical contact based on compact hardware and a simple control method. We demonstrated parallel translation and fabrication of a stacked structure of microscopic particles, on the surfaces of which a lot of DNA molecules are bound. A method for reactions of DNA using an optical technique has also being developed. The method is based on control of the temperature of a local small volume of a DNA solution, which is put on a substrate coated with light-absorbing material, by irradiating with laser beams. We irradiated the substrate or a bead, on which DNA molecules were attached by hybridization, and succeeded in detaching DNA from the substrate or the bead. These techniques are expected to contribute miniaturization and weight-reduction of information systems for computing, genome analyses, and other applications.

Space Lasers are vital tools for NASA's space missions and military applications. Although, lasers are highly reliable on the ground, several past space laser missions proved to be short-lived and unreliable. In this communication, we are shedding more light on the contamination and radiation issues, which are the most common causes for optical damages and laser failures in space. At first, we will present results based on the study of liquids and subsequently correlate these results to the particulates of the laser system environment. We present a model explaining how the laser beam traps contaminants against the optical surfaces and cause optical damages and the role of gravity in the process. We also report the results of the second harmonic generation efficiency for nonlinear optical crystals irradiated with high-energy beams of protons. In addition, we are proposing to employ the technique of adsorption to minimize the presence of adsorbing molecules present in the laser compartment.

Ion irradiation of polymer films is a promising process technology for photonics applications that require flexible, lightweight devices resistant to selected environmental variables. Crossed phase gratings that may serve as laser-beam array generators are fabricated using the dry process of irradiation of acrylic (PMMA) films with various doses of high-energy alpha particles through a stencil mask. The gratings are examined with the aid of AFM and SEM images, and Raman-Nath diffraction analysis is applied to estimate the generated refractive-index modulation as a function of the dose. SEM images of a stained grating cross-section suggest a mechanism of unsaturated bond formation and accompanying contraction of the irradiated polymer. Post-irradiation baking is shown to increase the contraction or generated surface relief by around an order of magnitude. Since the index modulation and surface relief due to irradiation tend to cancel, the overall diffraction effciencies of unbaked gratings do not surpass 67%, although baked gratings can provide higher diffraction effciencies.

The wide variety of optoelectronics applications in NASA flight systems and instruments require that optoelectronic technologies meet the demanding requirements of the space environment throughout mission life. These requirements vary widely from intense radiation near Jupiter to the very cold temperatures on the Martian surface to the effects of solar flares in Earth orbit. Considerable work has been performed under the NEPP Program to meet these assurance needs and minimize the risk of insertion of optoelectronics in NASA systems. In this paper we provide recent examples of this work for a variety of NASA mission applications that employ various optoelectronic devices.

We report on the design, fabrication and integration of micro/nano-scale optical wire circuit arrays and devices for high-speed, compact, light-weight, low power optical printed circuit boards (O-PCBs) and VLSI photonic applications. The optical wires are formed in the form of waveguides by thermal embossing and ultraviolet (UV) radiated embossing of polymer materials. The photonic devices include vertically coupled surface emitting laser (VCSEL) microlasers, microlenses, 45-degree reflection couplers, directional couplers, arrayed waveguide grating structures, multimode interference (MMI) devices and photodetectors. These devices are optically interconnected and integrated for O-PCB assembly and VLSI micro/nano-photonics. The O-PCBs are to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards or substrates. We report on the result of the optical transmission performances of these assembled O-PCBs. For the design, fabrication, and VLSI integration of nano-scale photonic devices, we used photonic crystal structures and plasmonic metallic waveguide structures. We examined the bandwidth, power dissipation, thermal stability, weight, and the miniaturization and density of optical wires and the O-PCB module. Characteristics of these devices are also described.

We present laboratory measurements of the reduction in UV-to-visible/IR reflectivity (1200&angst; - 10,000&angst;) of optical surfaces due to 50&angst; - 500&angst; deposited layers of out-gassed molecular contaminants from 9 commonly used spacecraft/space instrument materials that include Apiezon-L hi-vacuum grease, Braycote-601EF lubricant, DC 704 silicon oil, EPOM rubber clad wire, PVC clad wire, Scotchweld 2216 epoxy, Uralane 5753 staking compound, Tefzel cable tie and Aeroglaze Z306 black paint on Kapton. Our results are compared with predictions from theoretical models currently being widely used throughout the space industry. Good agreement is found at UV wavelengths, but large differences occur at visible wavelengths. This latter effect is due to the application of Beer's Law, which ignores the non-negligible effect of reflectance scattering from the thin film of the contaminant.

Maintenance tasks of the future International Experimental Thermonuclear fusion Reactor (ITER) will require communication links between the remotely operated equipment in the reactor vessel and the control room, some of which need to be radiation tolerant up to MGy dose levels. As a key element of opto-electronic transceivers, we therefore assessed the DC behavior of a commercial-off-the-shelf (COTS) SiGe heterojunction bipolar transistor (HBT) under gamma radiation up to 15 MGy, with dose rates from 160 Gy/h to 27 kGy/h. Our in-situ measurements of the forward DC current gain (hfe) present a limited loss of about 30 % for a base current of 100 μA, with a dependence on the biasing conditions and a thermally activated recovery. These first ever reported results up to MGy levels allow us to design circuit-hardened driving electronics for both photonic transmitters and receivers, enabling high bandwidth communications applied in a fusion reactor environment.

Silica on Silicon (SoS) and Silicon on insulator (SOI) fabrication technologies are now yielding efficient photonic devices that have potential uses (e.g. routing and switching) in multigigabit optical backplane interconnect applications. The ever increasing demands for higher speed data handling and greater throughput on board both operational and experimental satellites necessitate an examination of these technologies for their robustness and performance in a space environment. One of the main environmental stressors on electronic and photonic components is the incident radiation flux. This paper reports results from the experimental testing of two classes of photonic devices; namely a SoS arrayed waveguide grating (AWG), and a SOI ring resonator. For a total ionizing dose of 300 kRad Co60 gamma irradiation, the SOI ring resonator showed induced spectral shifts as lower than 0.4 pm/kRad, and the SoS AWG showed a maximum shift of 0.03 pm/kRad in one channel. The relatively low AWG radiation sensitivity tempt us to say that these devices could be considered radiation hard for the telecom CL wavelength band (1550 nm) in which these measurements were made.

The radiation resistance of Yb-doped fiber lasers, especially regarding Yb fiber lasers varying in doping constituents and at different doping concentrations is largely unknown. This paper reports on the gamma-ray induced optical transmission responses of two identical optical fibers that differed in their Yb doping concentrations by two orders of magnitude. The relative amplified spontaneous emission and insertion loss measurements of the two Yb fibers lasers is examined following irradiation by gamma-ray photons with energies of 1.17 and 1.33 MeV. The fibers were observed to exhibit excellent radiation resistance to gammarays following irradiations performed at a nominal dose rate of 2.1 rad(Si) s-1 and to a total dose of approximately 97.1 krad(Si). Comparisons of irradiated Yb fiber responses with other reported irradiated Yb doped fibers is presented.

Triboluminescence (TL) is the emission of light due to crystal fracture and has been known for centuries. One of the most common examples of TL is the flash created from chewing wintergreen Lifesavers. Since 2003, the authors have been measuring triboluminescent properties of phosphors, of which zinc sulfide doped with manganese (ZnS:Mn) is an example. Preliminary results indicate that impact velocities greater than 0.5 m/s produce measurable TL from ZnS:Mn. To extend this research, the investigation of the emission spectrum was chosen. This differs from using filtered photodetectors in that the spectral composition of fluorescence can be ascertained. Previous research has utilized a variety of schemes that include scratching, crushing, and grinding to generate TL. In our case, the material is activated by a short duration interaction of a dropped mass and a small number of luminescence centers. This research provides a basis for the characterization and selection of materials for future spacecraft impact detection schemes.

We present a calibration unit to be used in near and medium infrared instrumentation. The system belongs to the 'black-body' (BB) and 'integrating-sphere' (IS) category and has been developed during the phase-A study as part of the Medium Infrared Instrument (MIRI) to be inserted on the NASA-ESA mission James Webb Space Telescope (JWST). A voltage driven resistance temperature device (RTD) is used as active thermal light source with spectral energy distribution determined by the working temperature and material characteristics, while the integrating sphere is used in order to create a Lambertian beam of calibration light. The system would provide light both for flat-fielding calibration and, in a further development, for wavelength calibration making use of the same illumination optics.
We will describe the experimental setup and the properties requested by the device. A complete analytical simulation guiding the dimensioning of the emitter and IS is given with the results from several laboratory test made in order to qualify the system in realistic operating conditions.

In the Advanced Detectors Research Group of the Air Force Research Laboratory's Space Vehicles Directorate, we work to enhance existing detector technologies and develop new detector capabilities for future space-based missions, most often using photonic techniques. To that end, we present some ideas we are presently investigating: (i) tuning the wavelength response of detectors using applied electric or magnetic fields, (ii) detecting the full polarization vector of a signal within a single pixel of a quantum well detector, (iii) monolithic solid-state cooling of a detector using photoluminescence, and (iv) enhancement of weak electromagnetic fields using interactions with plasmons.

Space-born optical systems must be tolerant to radiation to guarantee that the required system performance is maintained during prolonged mission times. The radiation-induced absorption in optical glasses is often related with the presence of impurities, which are, intentionally or not, introduced during the manufacturing process. Glass manufacturers use proprietary fabrication processes and one can expect that the radiation sensitivity of nominally identical optical glasses from different manufacturers is different. We studied the gamma-radiation induced absorption of several crown glasses with nd ≈ 1.516 and vd ≈ 64, i.e. NBK7 (Schott), S-BSL7 (Ohara), BSC 517642 (Pilkington) and K8 (Russia). NBK7 recently replaced the well-known BK7. We therefore also compared the radiation response of NBK7 and BK7 glass. Our results show that whereas the glasses are optically similar before irradiation, they show a different induced absorption after irradiation and also different post-radiation recovery kinetics. Taking these differences into account can help to improve the radiation tolerance of optical systems for space applications.

Photo-thermo-refractive (PTR) glass is a new photosensitive material for phase hologram recording. This sodium-zinc-aluminum-silicate glass doped with silver, cerium and fluorine exhibits a refractive index modulation after exposure to UV radiation followed by a thermal treatment. Holographic volume gratings recorded in this glass show an absolute diffraction efficiency exceeding 97%, a thermal stability up to 400°C, and a high tolerance to laser radiation. These features support its application for laser beam control in optical communications and surveillance in space-born systems. A specific aspect of the space environment is the presence of ionizing radiation, which is known to influence the properties of optical materials. We studied the induced absorption in PTR glass after exposure to gamma radiation with doses exceeding 10 Mrad. The larger part of the induced absorption is found in the visible and UV spectral regions while in the infrared the absorption level remains sufficiently low to allow a long-term use of this material in space. In this paper, we discuss the structure of the induced absorption spectra in PTR glass and glass matrix which does not contain photosensitive agents.

Space instrument programs occasionally need an estimate of how dark current distribution of a silicon CCD changes versus proton radiation exposure and temperature. The task that is the subject of this article was started by adopting a relevant gamma distribution model produced by M.S. Robbins [1] and estimating its parameters, α and β, by using data acquired by Demara [2]. The fortuitous result was that α was found to depend solely on damage displacement dose and β was found to be practically equal to the native bulk dark current of silicon. These implications were tested with information from three published articles. In comparison with the published results, the model was found to be accurate within a factor of two.

Infrared interlevel electromagnetic response of different quantum
dot (QD) systems is investigated theoretically within the
self-consistent field approach. Individual QDs as well as lattices
of QDs electromagnetically interacting are considered. The Coulomb
interaction in the QD systems is shown to essentially affect the
optical spectra of the systems. Systems of QDs with uniaxial
rotation symmetry are considered. It is shown that the shape of QD
can dramatically affect the spectra, in particular, depending on
the polarization of incident radiation and number of electrons in
the dot. It is shown that the Coulomb interaction in the QD
systems causes the depolarization shift of the peak(s) in the
spectra, can affect the peak(s) height, and cause the peak split.
It is numerically established that the approximation of the point
dipole-dipole interaction can be used for adequate representation
of the effect of the dynamic interdot electron-electron
interaction on the spectra of the considered QD lattices. It
is found that the effects of the intradot and interdot Coulomb
interactions on the response can be analyzed separately. Effect of
the intradot electron-electron interaction on the spectra is
considered for different QD sizes and shapes. Illustrative maps of
the interlevel transitions are utilized to facilitate application
of the approach of the modified oscillator strength for
reproducing the absorption spectra of the considered QD
systems with interacting modes of the collective excitation. The
results obtained can be useful for designing nanooptoelectronics
devises based on the QDs, and engineering composite materials
including the QDs with predermined optical properties.

We will present our advance in the utilization of a non-lithographic approach for formation of periodic nanosized arrays and formation of hybrid structures suitable for light detection. We explore a self-organization process for formation of periodical nanopores in anodized aluminum oxide, the transfer of this pattern, and the subsequent growth within the pores. This approach was successfully demonstrated for a system having carbon nanotubes as kernel. The carbon nanotubes by themselves are very attractive for detector applications. It is theoretically predicted and experimentally proven that their band gap is adjustable in broad spectral range, their charge carrier mobility is high, and their thermal and mechanical properties are unmatched by other materials. The nanotemplate we use for growth of the nanotubes allows their controlled placement in a regular array, without restriction of the curvature of the surface to be covered. There are no principal limitations for scaling of the process. The third element of our approach is the integration with silicon which provides the compatibility with the well elaborated silicon technology. We will demonstrate the suitability of these structures for light detection.

We report the first two-color 320 x 256 infrared Focal Plane Array (FPA), based on a voltage-tunable InAs/InGaAs/GaAs DWELL structure. The detectors, grown by solid source molecular beam epitaxy (MBE) comprise of a 15-stack asymmetric DWELL structure sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The DWELL region consists of a 2.2 monolayer deposition of n-doped InAs quantum dots (QDs) in an In0.15GaAs0.85As well, itself placed in GaAs. The well widths below and above the dots are 50&angst; and 60&angst;, respectively. The absorption region asymmetry results in a bias dependent spectral response, with the peak wavelength varying from 5.5 to 10 μm. Using calibrated black body measurements, mid-wavelength and long wavelength specific detectivities (D*) of top-illuminated test pixels at 78K were estimated to be 7.1 x 1010 cmHz1/2/W (Vb= 1.0V) and 2.8 x 1010 cmHz1/2/W (Vb= 2.5V), respectively. Subsequently, a 320 x 256 QDIP FPA array was fabricated on a 30 μm pitch and was hybridized with an Indigo 9705 ROIC. Thermal imaging was successfully carried out at an estimated FPA temperature of 80K, using different optical filters between 3-5 μm, and 8-12 μm, so as to demonstrate two-color operation. The operability of the FPA was greater than 99%, and the noise-equivalent temperature difference was estimated to be less than 100 mK for f#1 (3-5 μm) and f#2 (5-9 μm) optics.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews